Fan Controller and Image Forming Apparatus

ABSTRACT

A fan controller and an image forming apparatus are provided. The fan controller includes a rotational frequency instructing unit configured to output driving instructions to a fan driving unit that is configured to control a rotational frequency of a fan, the driving instructions including a target value of the rotational frequency of the fan; a rotational frequency detection unit configured to detect an actual measurement value of the rotational frequency of the fan; a storage unit configured to store consecutively at given time intervals a plurality of parameters indicating a correspondence relationship between the driving instructions output by the rotation frequency instructing unit and the rotational frequency detected by the rotational frequency detection unit; and a notification unit configured to notify a condition of the fan on the basis of the plurality of parameters. The image forming apparatus includes a fan, a fan driver and the fan controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No.2008-050263 filed on Feb. 29, 2008, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

Apparatuses and devices consistent with the present invention relate tocontrolling a fan and, more particularly, to controlling a fan used inan image forming apparatus whereby a condition of the fan is monitored.

BACKGROUND

In the related art, a fan is often provided to cool various types ofapparatuses including an image forming apparatus. Japanese PublishedUnexamined Patent Application No. 2006-280162 describes maintaining arotational frequency of a related art fan by reducing a number ofresistance elements when the consumption of current of the fan increasesover a length of time.

However, the related art fan has a disadvantage in that, if theconsumption of current of the fan is great at a certain point in time,it is impossible to carry out control of the rotational frequency of thefan at a later time on the basis of past conditions.

SUMMARY

Exemplary embodiments of the present invention address the abovedisadvantages and other disadvantages not described above. However, thepresent invention is not required to overcome the disadvantagesdescribed above, and thus, an exemplary embodiment of the presentinvention may not overcome any of the disadvantages described above.

Accordingly, illustrative aspects of the present invention provide a fancontroller capable of notifying a condition of the fan on the basis ofconditions of the fan and an image forming apparatus in which the fancontroller is used.

According to an aspect of the present invention, there is provided a fancontroller comprising a rotational frequency instructing unit configuredto output driving instructions to a fan driving unit that is configuredto control a rotational frequency of a fan, the driving instructionscomprising a target value of the rotational frequency of the fan; arotational frequency detection unit configured to detect an actualmeasurement value of the rotational frequency of the fan; a storage unitconfigured to store consecutively at given time intervals a plurality ofparameters indicating a correspondence relationship between the drivinginstructions output by the rotation frequency instructing unit and therotational frequency detected by the rotational frequency detectionunit; and a notification unit configured to notify a condition of thefan on the basis of the plurality of parameters.

According to another aspect of the present invention, there is providedan image forming apparatus comprising a fan; a fan driver; and a fancontroller. The fan driver is configured to control a rotation frequencyof the fan. The fan controller comprises a rotational frequencyinstructing unit which outputs driving instructions to the fan driver,the driving instructions comprising a target value of the rotationalfrequency of the fan; a frequency detector which detects an actualmeasurement value of the rotational frequency of the fan; a memory whichconsecutively at given time intervals stores a plurality of parametersindicating a correspondence relationship between the drivinginstructions output by the rotational frequency instructing unit and therotational frequency detected by the frequency detector; and anotification unit which indicates a condition of the fan on the basis ofthe plurality of parameters.

According to yet another aspect of the present invention, there isprovided a fan controller comprising an integrated circuit comprising arotational frequency instructing circuit which outputs drivinginstructions to a fan driver that is configured to control a rotationalfrequency of a fan, the driving instructions comprising a target valueof the rotational frequency of the fan; a frequency detector whichdetects an actual measurement value of the rotational frequency of thefan; a memory circuit which consecutively at given time intervals storesa plurality of parameters indicating a relationship between the drivinginstructions output by the rotational frequency instructing circuit andthe rotational frequency detected by the frequency detector; and anotification circuit which indicates a condition of the fan on the basisof the plurality of parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the appearance of an image formingapparatus according to an exemplary embodiment of the present invention;

FIG. 2 is a circuit diagram showing an example of a constitution of adriving system according to an exemplary embodiment of the presentinvention;

FIG. 3 is a circuit diagram showing an example of a constitution of adriving system according to another exemplary embodiment of the presentinvention;

FIG. 4 is a view for explaining a relationship between drivinginstructions and a rotational frequency in each of the driving systems;

FIG. 5 is a flow chart showing control processing for the fan accordingto an exemplary embodiment of the present invention; and

FIG. 6 is a view for explaining relationships of various values in thecontrol processing.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

Next, a description will be given for an exemplary embodiment of thepresent invention by referring to the drawings. In this exemplaryembodiment, the present inventive concept is applied to an image formingapparatus.

1. Image Forming Apparatus

FIG. 1 is a perspective view showing the appearance of an image formingapparatus 1 of the present exemplary embodiment. The image formingapparatus is embodied as a laser printer 1. The laser printer 1 isinstalled, with the upper side on the page space given as the upper sidein the gravitational direction, and usually used, with the left nearside on the page space given as the front side.

The laser printer 1 includes a housing 3 formed approximately in a boxshape (rectangular solid shape). A paper discharging tray 5 on which aprinted medium that has been printed and discharged from the housing 3is provided on the upper face of the housing 3. In the present exemplaryembodiment, paper and sheets such as overhead projector (OHP) sheets areused as printed media. Alternatively, other types of paper and sheetsmay be used.

The paper discharging tray 5 is constituted to give an inclined face 5 awhich is inclined in such a manner as to lower from the upper face ofthe housing 3 to the rear side. A discharge portion 7 at which theprinted medium completed for printing is discharged is provided at therear end of the inclined face 5 a.

An upper cover 9 formed in approximately a U-letter shape so as toenclose the paper discharging tray 5 (inclined face 5 a) of the housing3 is provided with a line switch 1 a for switching the connection of thelaser printer 1 to, e.g., a network. The laser printer 1 is alsoprovided with a job cancellation switch 1 b for forcibly terminating(discontinuing) printing, a display panel 1 c as one example of anotification unit configured to display various types of information,and others. Alternatively, the notification unit may be a unitconfigured to generate a notification signal or an output pin on theASIC 50 which is connected to an external notification device, such as adisplay, light emitting diode (LED), or audible alarm.

The laser printer 1 is provided at the lower part of the housing 3 witha paper feeding cassette 11 which may be attached to or detachedtherefrom. There is provided inside the housing 3 a printer engine (notillustrated) which forms (prints) an image on a printed mediumaccommodated in the paper feeding cassette 11 by an electro-photographicprocess and discharges the printed medium from a discharge portion 7.Further, on the side face of the housing 3, there are provided fans 41,42 for cooling the printer engine or the power section, etc.,accommodated inside the housing 3. Two fans 41, 42 are shown in FIG. 1.However, alternatively, one fan or a plurality of fans may be provided.

2. Driving System of the Fan

Next, a description will be given of an example of a constitution of adriving system of the fans 41, 42. The driving system is an example ofthe fan controller. In addition, since the driving system of the fans41, 42 are substantially similar in constitution, only the drivingsystem of the fan 41 will be hereinafter described.

FIG. 2 is a circuit diagram showing an example of a constitution of thedriving system of the fan 41. As shown in FIG. 2, the fan 41 (FAN) iscontrolled by an application specific integrated circuit (ASIC) 50equipped with a central processing unit (CPU) 51, a read only memory(ROM) 52 and a random access memory (RAM) 53. The CPU is an example of arotational frequency instructing unit. A Frequency Generator (FG) signalis input from the fan 41 to an FGIN terminal. The FGIN terminal is anexample of a rotational frequency detection unit of the ASIC 50. Inaddition, the display panel 1 c is also connected to the ASIC 50.Further, the ASIC 50 is provided with a FAN_H terminal for driving thefan 41 at a high speed, a FAN_M terminal for driving the fan 41 at amedium speed, and a FAN_L terminal for driving the fan 41 at a lowspeed. The FAN_H terminal, the FAN_M terminal and the FAN_L terminalsuppply a driving voltage to an input terminal FAN_IN of the fan 41 viaa driving circuit 60. Specifically, the FAN_H terminal, the FAN_Lterminal, the FAN_M terminal and the driving circuit 60 correspond to afan driving unit.

A detailed description will now be given of an example of a constitutionof the driving circuit 60. As shown in FIG. 2, the FAN_H terminal isconnected via a resistor R2 to a base of a transistor Tr1 in which thebase is connected to an emitter via a resistor R1. The emitter of thetransistor Tr1 is grounded, and a collector is connected via a resistorR4 to a base of a transistor Tr2 in which the base is connected to anemitter via a resistor R3. The emitter of the transistor Tr2 isconnected to a direct current power source. A 24V direct current powersource is shown in FIG. 2. However, the specific value of the directcurrent power source may be different. The collector of the transistorTr2 is connected to the input terminal FAN_IN of the fan 41. Therefore,when an “H” level signal is output from the FAN_H terminal, an directvoltage, which is approximately equal to the voltage of the directcurrent power source (in this case, 24V) is supplied to the inputterminal FAN_IN, thus making it possible to drive the fan 41 at a highspeed.

The FAN_M terminal is connected via a resistor R7 to a base of atransistor Tr3 in which the base is connected via a resistor R6 to anemitter. The emitter of the transistor Tr3 is grounded, and a collectoris connected via a resistor R9 to a base of a transistor Tr4 in whichthe base is connected via a resistor R8 to an emitter. The emitter ofthe transistor Tr4 is connected via a Zener diode D1 to the directcurrent power source, and the collector is connected to the inputterminal FAN_IN of the fan 41. Thus, when an “H” level signal is outputfrom the FAN_M terminal, a direct voltage obtained by subtracting avoltage drop due to the Zener diode D1 from the voltage of the directcurrent power source (in this case 24V) is supplied to the inputterminal FAN_IN, thus making it possible to drive the fan 41 at a mediumspeed.

The FAN_L terminal is connected via a resistor R12 to a base of atransistor Tr5 in which the base is connected via a resistor R11 to anemitter. The emitter of the transistor Tr5 is grounded, and a collectoris connected via a resistor R14 to a base of a transistor Tr6 in whichthe base is connected via a resistor R13 to an emitter. The emitter of atransistor Tr12 is connected via Zener diodes D2, D3 to the directcurrent power source, and the collector is connected to the inputterminal FAN_IN of the fan 41. Thus, when an “H” level signal is outputfrom the FAN_L terminal, a direct current voltage obtained bysubtracting a voltage drop due to the Zener diodes D2, D3 from thevoltage of the direct current power source (in this case 24V) issupplied to the input terminal FAN_IN, thus making it possible to drivethe fan 41 at a low speed. Another driving terminal, such as, e.g., asuper low driving terminal and circuit (three Zener diodes are connectedin series) may be also provided.

FIG. 3 shows an example of a constitution of the driving circuitaccording to another exemplary embodiment of the present invention. InFIG. 2, an instance where an analog direct current voltage is suppliedto the input terminal FAN_IN of the fan 41 was illustrated. However,alternatively, a pulse width modulated (PWM) signal may be input to theinput terminal FAN_IN of the fan 41 to drive the fan. In such a case,the driving system of the fan 41 may be constituted as shown in FIG. 3.Specifically, in this case, a control (CTL) signal as the PWM signal isdirectly input from a FAN_CTL signal terminal of the ASIC 50 to theinput terminal FAN_IN of the fan 41, thus making it possible to drivethe fan 41 at a speed corresponding to the duty ratio of the CTL signal.

3. Control Processing of the Fan

In either instance, as shown in FIG. 4, the greater the voltage input tothe fan 41 or the greater the duty ratio (PWM DUTY) of the CTL signalinput to the FAN 41, the more the rotational frequency of the fan 41increases. The rotational frequency of the fan 41 will increasesubstantially in proportion to the voltage or the duty ratio until therotational frequency reaches a certain value, and will not increase anymore when the rotational frequency reaches the certain value.

A value R obtained by dividing the rotational frequency by the voltageor the duty ratio is adopted as a parameter indicating a correspondencerelationship between the driving instructions (the voltage or dutyratio) input to the fan 41 and a rotational frequency of the fan 41,thereby executing the control shown below.

FIG. 5 is a flow chart of control processing according to an exemplaryembodiment of the present invention. The control processing is providedto the fan 41. The control processing is started at a time when thelaser printer 1 is switched on and the fan 42 is also controlledsimilarly and concurrently. Further, the above-described parameter R isstored in a log in chronological order in the RAM 53 during theexecution of the control processing. Specifically, the logs ofparameters R are stored in the RAM 53 at given time intervals while theimage forming apparatus is powered on. If a new parameter R is to bestored after a given number of the parameters R are stored in the RAM53, an oldest one of the parameters R in the RAM 53 is erased and thenthe new parameter R is stored in the RAM 53. The RAM 53 is one exampleof a storage unit.

As shown in FIG. 5, in the control processing, in S1, the fan 41 isfirst rotated and driven. In S2, counters Nh and N1 to be describedlater are reset to 0. In S3, it is determined whether R is greater thana value Rmax. If it is determined that R is greater than the thresholdvalue Rmax (S3: Y), an error message, such as “Fan error” and/or “Call atechnician” is displayed on the display panel 1 c. Then, the processingproceeds to S5. In S5, the laser printer 1 as a whole including the fan41 is halted and the processing is temporarily completed. On the otherhand, if it determined that R≦Rmax, (S3: N), the processing proceeds toS6, and it is determined whether R is less than a minimum value Rmin. Ifit is determined that R<Rmin (S6: Y), the processing proceeds to theabove-described S4, and if it is determined that R≧Rmin (S6: N), theprocessing proceeds to S10.

In S10, it is determined whether R is greater than an upper limit Rh. Rhdenotes a value at which the value R is deviated towards a higherrotational frequency within a permissible range. If it is determinedthat R≦Rh (S10:N), a counter Nh is reset to be 0 in S11, and theprocessing proceeds to S20 to be described later. On the other hand, ifit is determined that R>Rh (S10:Y), the counter Nh is incremented by onein S12, and it is determined whether the counter Nh is in excess of 100in S13. If it is determined that Nh≦100 (S13:N), the processing proceedsto S20. If it is determined that the counter Nh>100 (S13:Y), an errormessage such as, e.g., “Fan error” and/or “Call a technician” isdisplayed on the display panel 1 c, and the processing proceeds to thepreviously described S5. In other words, the counter Nh is a counter forcounting the number of times at which R is consecutively in excess of anupper limit Rh of the target value within a threshold range (e.g.,Rmin≦R≦Rmax). In this case, the number of times is set at 100. However,the number of times may be set to a different threshold number.

In S20, it is determined whether R is less than a lower limit R1. R1denotes a value at which the value R is deviated towards a lowerrotational frequency within a permissible range. If it is determinedthat R≧R1 (S20:N), the counter N1 is reset to be 0 in S21, and theprocessing proceeds to S30 to be described later. On the other hand, ifit is determined that R<R1 (S20:Y), the counter N1 is incremented by onein S22, and it is determined whether the counter N1 is in excess of 100.If it is determined that the counter N1>100 (S23:Y), an error messagesuch as “Fan error” and/or “Clean the fan” is displayed on the displaypanel 1 c, and the processing proceeds to the previously described S5.In other words, the counter N1 is a counter for counting a number oftimes at which R is consecutively in excess of a lower limit R1 of thetarget value within a threshold range (Rmin≦R≦Rmax). In this case, thenumber of times is set at 100. However, the number of times may be setto a different threshold number.

If it is determined that the counter N1≦100 (S23:N), it is determinedwhether a difference d obtained by subtracting the previously obtained Rfrom the presently obtained R is lower than a threshold value of thedifference (negative value) D. If it is determined that the difference dis lower than the threshold value D (S25:Y), an error message such as“Fan error” and/or “Call a technician” is displayed on the display panel1 c, and the processing proceeds to the previously described S5. On theother hand, if it is determined that D≦d (S25:N), it is determinedwhether a value obtained by doubling the presently obtained R is lowerthan an average value (Rave) of R so far obtained. If it is determinedthat 2R<Rave (S27:Y), an error message such as “Fan error” and/or “Calla technician” is displayed on the display panel 1 c, and the processingproceeds to the previously described S5.

On the other hand, if it is determined that 2R≧Rave (S27:N), theprocessing proceeds to S30. In S30, after a standby period, theprocessing proceeds to the previously described S3. The standby periodmay be approximately one hour, or another period.

Due to the control processing according to an exemplary embodiment ofthe present invention, it is possible to notify in detail as describedbelow a condition of the fan 41 on the basis of a plurality of theparameters R stored in chronological order. That is, as shown in FIG. 6,R is set so as to be between target values Rh, R1 and within a thresholdrange specified by Rmax, Rmin. Specifically, there are set a medianvalue R0 and an upper limit Rh and a lower limit R1 of a range in whichthe target value R can be regarded as the median value R0. The thresholdrange is, for example, a permissible range which is be determined as arange in which the fan normally operates. In addition, in FIG. 6, thelongitudinal axis is given as “rotational frequency/voltage,” whichcorresponds to the driving system shown in FIG. 2. Thus, where thedriving system shown in FIG. 3 is adopted, the longitudinal axis isgiven as “rotational frequency/duty ratio.”

Then, a case in which R is outside of the target values and thethreshold range (S3:Y or S6:Y, i.e., R>Rmax or R<Rmin), the ASIC 50determines as an error to display the error, thereby halting theapparatus (S4, S5). Further, a case in which R is within the thresholdrange but remains higher than the upper target value (i.e., Rmin≦R≦Rmax,and R>Rh) for a certain period of time or longer (S13:Y), the ASIC 50determines that a driving circuit 61 for driving the fan 41 or the likefails, thus displaying an error, and halting the apparatus (S14,S5).

Further, a case in which R is within the threshold range but remainslower than the lower target value (i.e., Rmin≦R≦Rmax, and R≦R1) for acertain period of time or longer (S23:Y), the ASIC 50 determines thatthe contamination by foreign matter such as dust prevents the rotationof the fan 41, thus displaying an error requesting cleaning of the fan41 to halt the apparatus (S24,S5).

Still further, a case in which R decreases extremely (S25:Y or S27:Y),the ASIC 50 determines that an abnormality has occurred in whichsomething other than dust prevents the rotation of the fan 41, thusdisplaying an error to halt the apparatus (S26, S28, S5). Accordingly,it is possible to notify in detail a condition of the fan 41.

In addition, the present inventive concept shall not be limited to theabove-described exemplary embodiments in any way, but may be executed invarious exemplary embodiments within the scope of the appended claims.For example, in the above exemplary embodiments, where foreign mattersuch as dust prevents the rotation of the fan 41 (S23:Y), error messagessuch as “Fan error” and “Clean the fan” are displayed to halt theapparatus (S4,S5). However, such control may be executed that the fan 41is automatically rotated at a high speed for a time to remove the dustor the like. In such a case, where the fan 41 is rotated at a high speedduring a period of time, the time at which the fan 41 is rotated at highspeed may be staggered. For example, the fan may be rotated at highspeed when there are few people, for example, at midnight, or whenanother laser printer 1 is connected to the same network, or whencommunications are made between the laser printer 1 and another laserprinter 1. Thus, it is possible to reduce as much as possible noisegenerated in association with the rotation of the fan 41 at a highspeed.

Further, in the above-described exemplary embodiments, at operations S4,S14, S26, and S28, similar error messages are displayed. However, thedisplay of error messages in these operations may be made different. Forexample, error codes according to individual errors may be alsodisplayed, depending on causes of individual errors. Still further, thepresent inventive concept can be applicable to apparatuses other than animage forming apparatus or a laser printer. For example, the presentinventive concept is applicable to any apparatus which uses a fan. Inaddition to the above-described parameters, various parameters may beadopted.

Still further, the value (parameter) R is obtained by dividing therotational frequency by the voltage or the duty ratio. However, thevalue (parameter) R may be obtained by dividing an actual measurementvalue of the rotational frequency of the fan 41 by a target value of therotational frequency of the fan 41 instructed by the fan controller(ASIC 50).

According to exemplary embodiments of the present invention, a fancontroller is provided with a fan driving unit configured to inputdriving instructions to the fan, a rotational frequency detection unitconfigured to detect a rotational frequency of the fan, a storage unitconfigured to store in chronological order a plurality of parametersindicating a correspondence relationship between the drivinginstructions input by the fan driving unit and the rotational frequencydetected by the rotational frequency detection unit, and a notificationunit configured to notify a condition of the fan on the basis of theplurality of parameters stored by the storage unit.

The fan driving unit may provide driving instructions to a fan, therebydriving the fan. Further, the storage unit may store in chronologicalorder the plurality of parameters indicating a correspondencerelationship between the driving instructions input by the fan drivingunit and the rotational frequency detected by the rotational frequencydetection unit, and the notification unit may notify a condition of thefan on the basis of the plurality of parameters stored by the storageunit. Therefore, the notification unit is able to notify inchronological order in detail a condition of the fan on the basis of theplurality of parameters stored.

Alternatively, the fan controller according to exemplary embodiments ofthe present invention may be constituted in such a manner that whenvalues of the plurality of parameters stored by the storage unit aredeviated above a higher target range within a threshold rangeconsecutively for a given number of times, the notification unitnotifies an error corresponding to the condition thereof. In this case,the notification unit determinates a defective circuit or the like, thusmaking it possible to notify an error corresponding thereto.

Alternatively, the fan controller according to exemplary embodiments ofthe present invention may be constituted in such a manner that whenvalues of the plurality of parameters stored by the storage unit aredeviated below a lower target range within a threshold rangeconsecutively for a given number of times, the notification unitnotifies an error corresponding to the condition thereof. In this case,the notification unit determines that contamination by foreign mattersuch as dust has occurred, thus making it possible to notify an errorcorresponding thereto.

Alternatively, the fan controller according to exemplary embodiments ofthe present invention may be constituted in such a manner that whenvalues of the parameters stored by the storage unit change so as to bein excess of a threshold amount with respect to values of the parametersstored in the past, the notification unit notifies an errorcorresponding to the condition thereof. In this case, the notificationunit determines that the fan is prevented from being rotated due to anabnormality other than dust, thus making it possible to notify an errorcorresponding thereto. In addition, the values of the parameters storedin the past may be previously stored values, a mean value in the past orother values.

Still further, the above-described parameters may include variousparameters, for example a value obtained by dividing a rotationalfrequency detected by the rotational frequency detection unit by avoltage applied to the fan as the driving instructions by the fandriving unit, or a value obtained by dividing the rotational frequencyby a duty ratio of a PWM signal input to the fan as the drivinginstructions by the fan driving unit.

In addition, an image forming apparatus according to exemplaryembodiments of the present invention is that in which any one of theabove fan controllers is used. The thus constituted image formingapparatus is able to notify in detail as described above a condition ofthe fan which cools the interior thereof and others.

While the present invention has been shown and described with referenceto certain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A fan controller comprising: a rotational frequency instructing unitconfigured to output driving instructions to a fan driving unit that isconfigured to control a rotational frequency of a fan, the drivinginstructions comprising a target value of the rotational frequency ofthe fan; a rotational frequency detection unit configured to detect anactual measurement value of the rotational frequency of the fan; astorage unit configured to store consecutively at given time intervals aplurality of parameters indicating a correspondence relationship betweenthe driving instructions output by the rotation frequency instructingunit and the rotational frequency detected by the rotational frequencydetection unit; and a notification unit configured to notify a conditionof the fan on the basis of the plurality of parameters.
 2. The fancontroller according to claim 1, wherein when each of a given number ofconsecutively stored parameters of the plurality of parameters indicatesthat the actual measurement values are greater than the target value,the notification unit notifies an error corresponding to the conditionthereof.
 3. The fan controller according to claim 2, wherein when eachof a given number of consecutively stored parameters of the plurality ofparameters indicates that the actual measurement values are less thanthe target value, the notification unit notifies an error correspondingto the condition thereof.
 4. The fan controller according to claim 1,wherein when each of a given number of consecutively stored parametersof the plurality of parameters indicate that the actual measurementvalues are less than the target value, the notification unit notifies anerror corresponding to the condition thereof.
 5. The fan controlleraccording to claim 1, wherein when one parameter of the plurality ofparameters indicates that the actual measurement value is lower than thetarget value and also when a value of the one parameter indicates that adifference between the actual measurement value and the target value isgreater than a threshold value, the notification unit notifies an errorcorresponding to the condition thereof.
 6. The fan controller accordingto claim 1, wherein the driving instructions are a voltage applied tothe fan driving unit, and the parameter is a value obtained by dividingthe actual measurement value by the voltage.
 7. The fan controlleraccording to claim 1, wherein the driving instructions are a pulse widthmodulated (PWM) signal, and the parameter is a value obtained bydividing the actual measurement value by a duty ratio of the PWM signal.8. An image forming apparatus comprising: a fan; a fan driver configuredto control a rotation frequency of the fan; and a fan controllercomprising: a rotational frequency instructing unit which outputsdriving instructions to the fan driver, the driving instructionscomprising a target value of the rotational frequency of the fan; afrequency detector which detects an actual measurement value of therotational frequency of the fan; a memory which consecutively at giventime intervals stores a plurality of parameters indicating acorrespondence relationship between the driving instructions output bythe rotational frequency instructing unit and the rotational frequencydetected by the frequency detector; and a notification unit whichindicates a condition of the fan on the basis of the plurality ofparameters.
 9. A fan controller comprising: an integrated circuitcomprising: a rotational frequency instructing circuit which outputsdriving instructions to a fan driver that is configured to control arotational frequency of a fan, the driving instructions comprising atarget value of the rotational frequency of the fan; a frequencydetector which detects an actual measurement value of the rotationalfrequency of the fan; a memory circuit which consecutively at given timeintervals stores a plurality of parameters indicating a relationshipbetween the driving instructions output by the rotational frequencyinstructing circuit and the rotational frequency detected by thefrequency detector; and a notification circuit which indicates acondition of the fan on the basis of the plurality of parameters. 10.The fan controller according to claim 9, wherein the fan drivercomprises an external driving circuit which comprises a high voltageoutput circuit, a medium voltage output circuit, and a low voltageoutput circuit, wherein the rotational frequency instructing circuit iscoupled to the external driving circuit and controls the externaldriving circuit to output a high voltage, a medium voltage, or a lowvoltage, as the driving instructions, to the fan based on an output fromthe fan driver circuit.
 11. The fan controller according to claim 9,wherein the driving instructions comprise a pulse width modulatedsignal.
 12. The fan controller according to claim 11, further comprisinga controller, wherein when a value of the plurality of parametersexceeds a first threshold range, the controller controls thenotification circuit to indicate a first error and halts a rotation ofthe fan, when consecutive values of the plurality of parameters arewithin the first threshold range but exceed an upper limit of the targetvalue for a given number of times, the controller controls thenotification circuit to indicate a second error and halts the rotationof the fan, and when consecutive values of the plurality of parametersare within the first threshold range but decrease below a lower limit ofthe target value for a given number of times, the controller controlsthe notification circuit to indicate a third error and halts a rotationof the fan.